ABSTRACT
We consider the near-surface layer of the ocean as a thin layer with a thickness ranging from several metres to one or several tens of metres adjoining the free surface of the ocean directly from below and including this surface, the thermal boundary layer,* the diurnal (or daily) thermocline, and all the stratifications that arise because of higher frequency processes and non-periodic atmospheric effects. The near-surface layer absorbs solar radiation directly and reacts to heating, cooling, evaporation, and freshening due to direct local effects of the atmosphere as well as to near-surface water exchange between neighbouring areas. Conditions are created in this layer for the development and suppression of convection and turbulence. All this causes increased space and time variability of the main hydrophysical fields, whose statistical characteristics often surpass the variability indices of the same fields in the underlying layers of the ocean, with the exception of variability characteristics induced by internal waves on fixed horizons of the seasonal and main thermocline. The near-surface layer of the ocean with its increased concentration and specific composition of suspended matter forms the colour of the ocean, i.e. the spectral composition of radiation from the ocean. The lower boundary of the near-surface layer of the ocean is considered to be the lower boundary of the diurnal (daily) thermocline developing during daylight under relatively calm conditions of the sea. This boundary is not fixed by depth. By the time it has reached maximum development [about 1600-1800 local solar time (LST)], the near-surface layer usually contains ~ 90-95% of the daily solar heat absorbed by the ocean. The dynamics of the layer, as we will see below (see Chapter 5), is characterized mainly by non-stationary movements of various nature. The thickness of the near-surface layer coincides with that of the upper quasi-homogeneous layer (UQL) under intensive wind-wave and convective mixing.
